Resins reinforced with carbon fibers (carbon fiber reinforced plastics) are materials having light weight, high strength, and high elasticity. Carbon fiber reinforced plastics are applied to aircraft members and wind turbine blades, for example. Examples of carbon fiber reinforced plastics include matrixes of thermosetting resins (carbon fiber reinforced thermosetting plastics: CFRPs) and matrixes of thermoplastic resins (carbon fiber reinforced thermoplastics: CFRTPs). CFRTPs have an advantage in that they need a shorter molding time than CFRPs (high-cycle performance).
An aircraft member, for example, includes a portion where CFRTP members are bonded to each other, a portion where a CFRTP member and a thermoplastic-resin member are bonded to each other, or a portion where thermoplastic-resin members are bonded to each other. In order to take advantage of the high-cycle performance of CFRTPs, an adhesion technique for quickly bonding members is required.
Typical adhesives are mainly composed of thermosetting resins. An adhesive mainly composed of a thermosetting resin needs to be heated for use. However, for bonding between thermoplastic resins with the adhesive, the thermoplastic resins cannot be heated to the curing temperature of the thermosetting resin; thus, adequate adhesive strength cannot be ensured.
Another adhesion technique uses microwave induction heating. In this technique, a magnetic substance (e.g., ferrite) serving as a microwave heating element is mixed to the adhesive and the adhesive is cured using heat generated by the microwave heating element upon irradiation of the adhesive with microwaves.
PTL 1 uses an adhesive containing a filler made of carbon black or SiC. PTL 1 discloses a method of bonding two adherends by irradiating the adhesive with microwaves, so that the filler generates heat and the adhesive is cured.
Ultrasonic bonding is under study as a novel adhesion technique. In ultrasonic bonding, an adhesive containing an energy director is protrudingly attached to a portion of one resin member to be bonded, and the one resin member is then brought into contact with another resin member with the adhesive-applied portion facing downward. When the portion to be bonded is irradiated with ultrasonic waves from above the members, the energy director generates heat upon reception of ultrasonic waves and the adhesive melts, thereby bonding the members.